Automatic elevator car systems, i.e., systems in which the car door automatically opens when the car reaches a floor and close before the car leaves a floor, are well-known in the art. In such systems, the hoistway door may be automatically opened and closed or may be manually opened and closed. In such systems, there usually is a switch or switches operable when the hoistway door is closed and a switch or switches operable when the car door or gate is closed which permits the car hoisting apparatus to move the car to another floor when all switches have been operated. Also, such systems usually include locking circuits which prevent opening of the doors unless the car is substantially level with the floor at which the doors control entrance and egress from the car and include a safety edge on one or more of the doors to recycle the doors and prevent starting of a car from a floor when closing of a door is obstructed.
Such known systems operate satisfactorily when there is no deliberate interference therewith. However, juveniles, persons intending to commit robbery and others, find it exciting or convenient to interfere with the normal operation for mischievous or criminal reasons and learn how to disable a car, to prevent normal door operation or to leave open a hoistway door after the car has left the floor where the door is located.
For example, when the hoistway door is open, the switch or switches operable thereby are accessible to the knowledgeable. Although such opening of the door will, by reason of the conventional circuits, stop the associated car, the hoistway door switch, which is on the hoistway wall, may be disabled or by-passed intentionally, such as by a shunt, to permit the car to continue to operate or may be accidentally by-passed, such as by shorting thereof.
Similarly, the car door or gate switch or switches are accessible from the car doorway or the hoistway doorway, and if the switch or switches are disabled or by-passed, the car will move even if the door or doors of the car are not closed, creating a passenger hazard and permitting the car to be stopped and started by manipulation of the car door switch or switches.
Conventional elevator systems also may have either an automatic sliding or a manually operable, swinging hoistway door.
Many of such known systems are in use, and the main object of the invention is to permit the addition to such systems of relatively simple apparatus which will make it extremely difficult to tamper with normal operation of an elevator car including the malfunction of the circuits added thereto without causing the car to remain at the floor where the tampering or malfunction occurs and, preferably, causing the sounding of an alarm. However, the principles of the invention are also applicable to newly installed elevator systems.
It has heretofore been proposed for elevator systems having swinging hoistway doors that duplicate hoistway or floor door switches be added at the floors of a building which are inaccessible from the car or hoistway door and which are protected to prevent movement of a car when the normal floor door switches are tampered with or are accidentally by-passed. However, such duplicate switches must be installed in the hoistway with separate wiring and protect against only by-passing of the floor door operated switches. Also, such duplicate, or back-up, switches are operated at the same time as the normal switches and if similar switches are used in elevator systems having power operated, sliding, hoistway doors, the car would be stopped at a floor with the doors closed thereby preventing passenger egress without further action by a passenger or supervisory personnel.
In my prior art U.S. Pat. No. 4,108,281, I have disclosed a door tampering protection system which is satisfactory for preventing operation of an elevator car under the described tampering situations, but there are other situations, such as malfunctions of a portion or portions of the protection circuits, serviceman errors, etc., to which it is highly desirable that the protection circuit be responsive. Furthermore, it is desirable to simplify the circuit of said U.S. Pat. No. 4,108,281 insofar as the functions performed thereby are concerned.
For example, standard elevator circuits have the gate, or floor door, switch and the car door lock circuits connected in series, and because the gate switch closes first as the doors close, door lock tampering or shorted door contacts cannot be sensed until the gate switch closes.
The door movement between closing of the gate switch and the closing of the door contacts is 11/2 inches or less, and in such amount of movement, tampering must be detected and the door movement altered, e.g. reversed. It is possible, by manually forcing the door to close, to allow the car to run. Also, in the circuit of said U.S. Pat. No. 4,108,281, if there is an open circuit or coil failure, such failures are undetected and protection is lost.
In addition, while two switches responsive to gate and door conditions can be used in the present invention, as in the circuit of said U.S. Pat. No. 4,108,281, the circuit of the preferred embodiment of the present invention permits the elimination of one of the switches.